Acid rain, ozone depletion led to mass extinction 250m yrs ago

Acid rain and ozone depletion fuelled extinction of 90 per cent of marine species and 70 per cent terrestrial species around 250 million years ago, a new study has found.
At the end of the Permian period, there was a mass extinction so severe that it remains the most traumatic known species die-off in Earth's history.
Some researchers have suggested that this extinction was triggered by contemporaneous volcanic eruptions in Siberia.
New results from a team including Director of Carnegie Institution's Department of Terrestrial Magnetism Linda Elkins-Tanton show that the atmospheric effects of these eruptions could have been devastating.
The mass extinction included the sudden loss of more than 90 per cent of marine species and more than 70 per cent of terrestrial species and set the stage for the rise of the dinosaurs.

The fossil record suggests that ecological diversity did not fully recover until several million years after the main pulse of the extinction.

One leading candidate for the cause of this event is gas released from a large swath of volcanic rock in Russia called the Siberian Traps.
Using advanced 3-D modelling techniques, the team, led by Benjamin Black of the Massachusetts Institute of Technology, was able to predict the impacts of gas released from the Siberian Traps on the end-Permian atmosphere.
Their results indicate that volcanic releases of both carbon dioxide (CO2) and sulphur dioxide (SO2) could have created highly acidic rain, potentially leaching the soil of nutrients and damaging plants and other vulnerable terrestrial organisms.

Releases of halogen-bearing compounds such as methyl chloride could also have resulted in global ozone collapse.
The volcanic activity was likely episodic, producing pulses of acid rain and ozone depletion.
The team concluded that the resulting drastic fluctuations in pH and ultraviolet radiation, combined with an overall temperature increase from greenhouse gas emissions, could have contributed to the end-Permian mass extinction on land.
The study was published in the journal Geology.